How to Terraform a Dead Earth
In the foreseeable future, a scientific community has discovered an alternate universe in which the solar system centers around a binary system of G-type suns, unlike the one G-type that ours orbits. The first planet is a diamond-crusted carbon planet twice as wide and eight times as massive as Earth, orbiting the second star from a distance of 1.1 million miles. The second planet is a Venus-like planet 175% as wide and five-and-a-half times as massive as Earth, orbiting both stars from a distance of 109 million miles. In the habitable zone is the third planet, an Earth-like planet 5800 miles wide with the following features:
A gravity 75% that of Earth
A retrograde rotation (suns rise from the west and set in the east) of 42 hours, a cycle that must be completed 827 times to make up one revolution (an "Asgardian" year)
A single moon 3,474.2 miles wide and orbiting "Asgard" from a distance of 384,400 miles An axial tilt varying from 109.7 to 118.32 degrees every 1.4 million years
This alternate Earth is also more volcanically active, as indicated in the dimensions of its oceans:
Shallow seas cover 40% of the oceans
Deep seas cover 32% of the oceans
Trenches and deeps cover 15% of the oceans
Abyssal plains are the smallest feature of this alternate Earth's oceans, covering only 13%
The atmosphere consists primarily of carbon dioxide and methane, but it still has 2% as much oxygen as our Earth.
In every respect, it should have life. The problem with that is that it used to have life, but we have just missed a mass extinction severe enough to wipe the slate clean.
This is a map of "Asgard". The red presented at the bottom of the map is the cause of the crisis that wiped out all life--a large basaltic plateau representing a volume of 80,000,000 cubic miles and a maximum elevation of 9,800 feet. Such a series of eruptions would have released enough greenhouse gases to wipe out even the toughest of organisms. So this Earth-like planet is too extreme for our first wave of terraforming pioneers, blue-green cyanobacteria, to thrive. Through a combination of natural and manmade means, how do we cool down the planet and possibly dilute the acidity of the oceans to the extent of making cyanobacterial colonization possible?